Neutral section insulator

ABSTRACT

In a neutral section ( 1 ) for use with an overhead railway conductor line, which neutral section ( 1 ) is disposed between the ends of the conductor line when in use and comprises an insulator ( 10 ) to isolate the ends of the conductor line from each other, the neutral axis of the neutral section ( 1 ) being such that when the neutral section ( 1 ) is in use the neutral axis is aligned closely with the neutral axis of the conductors on its either side and the height of the insulator ( 10 ) is chosen so that the stiffness and the dynamic mass of the neutral section ( 1 ) closely match those of the conductors, on its either side in both the vertical and horizontal planes.

REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase under 35 U.S.C. §371 ofInternational Application No. PCT/GB2004/002251, having an internationalfiling date of May 27, 2004, and claims priority of United KingdomApplication No. UK032831.1, filed Jun. 4, 2003, and UK0405412.8, filedMar. 10, 2004.

FIELD OF THE DISCLOSURE

The present invention relates to a neutral section insulator for use inconjunction with railway overhead conductor lines.

BACKGROUND

Electric trains are powered through overhead copper conductor lines, thepower being conveyed via a pantograph attached to the roof of the train.The conductor lines are usually powered by 25 kV AC supplied from powerstations along the route of the lines. As the power stations are notsynchronised, a peak-to-peak difference of up to 50 kV AC can occurwhere two power supplies meet along the length of a conductor line. Itis important to ensure that the pantograph does not register thedifference in power supplies as otherwise a large electrical load wouldbe placed on it, which could damage it and other electrical equipment inthe train. As it is impractical to synchronise the power stations, theyare normally isolated from each other by the provision of an assemblyknown as a neutral section insulator on each conductor line.

It is desirable that the pantograph does not detect the presence of theneutral section insulator on the conductor lines as, apart fromelectrical loading, it would then also be subject to variable reactionforces, which would be conveyed to the train to cause “humping”.

The neutral section insulators that are currently on the market includethose provided by Siemens GmbH, Arthur Flury AG and Furrer & Frey AG.The neutral section insulator of Siemens GmbH, consisting of twoinsulator body rods mounted on plates with copper conductors beingclamped thereto, is mechanically quite different from the conductors andincreases the scope of shock loading on the pantograph. Although theheight of the neutral section insulator can be adjusted relative to thecopper conductors in order to align them as closely as possible in thevertical plane, the catenary member that is used for such adjustmentmakes the neutral section insulator assembly more bulky, increases itsstructural and mechanical difference from the conductor lines, andcomplicates its installation. An arcing horn is provided in this neutralsection insulator to channel the power dissipation that occurs if thepantograph registers the difference in power supplies. However, it isnot particularly effective in this role, as often sparks are seen toform where the pantograph attaches to the neutral section insulator.Furthermore, this neutral section insulator is expensive, wears quickly(it needs to be replaced roughly every eight months), and requiresmonthly maintenance to turn the insulator body sections (which wear outby virtue of point contact with the pantograph).

Accordingly, it is desirable to provide a neutral section insulator thateffectively isolates the conductor lines without posing a “gap” to apantograph traversing the length of the lines, is maintenance-freeduring the lifetime of the product, cheap to produce and simple toinstall.

According to an embodiment of the present invention, there is provided aneutral section insulator for use with an overhead railway conductorline, which neutral section insulator is disposed between the ends ofthe conductor line when in use and comprises an insulator body toisolate the ends of the conductor line from each other; wherein theneutral axis of the neutral section insulator is such that when theneutral section insulator is in use the neutral axis is aligned closelywith the neutral axis of the conductors on its either side and theheight of the insulator body is chosen so that the stiffness and thedynamic mass of the neutral section insulator closely match those of theconductors on its either side in both the vertical and horizontalplanes.

The structural and mechanical profile of a neutral section insulatorembodying the present invention is constructed to closely correspondwith that of railway overhead copper conductor lines in order tominimise the scope of being registered by a pantograph, this beingachieved by closely aligning the neutral axes (median bending line) ofthe neutral section insulator and the conductors on its either side, andby closely matching the stiffness and the dynamic mass of the neutralsection insulator and the conductors in both the vertical and horizontalplanes.

An embodiment of the present invention provides a continuous runningsurface to the pantograph that is both coplanar with the conductors onits either side (so that the pantograph is not subject to shock loading)and narrow (since misalignment with the pantograph would cause a severetwisting action in the neutral section insulator), and also provides theadvantage that the drag imposed by the neutral section insulator on thepantograph is equal to, or less than, that exerted on it by theconductors.

Furthermore, an embodiment of the present invention provides isolationover a distance in excess of 1.5 m, even when the pantograph (which is0.2 m in width) attaches to the neutral section insulator andeffectively increases its length to about 1.7 m.

An embodiment of the present invention is capable of withstanding the 15kN loads, which are hung every few hundred meters along the length ofthe conductor lines in order to provide tension, without degrading.

An embodiment of the present invention provides all the above-discussedadvantages in adverse environmental conditions such as rain, snow,contamination, etc.

BRIEF DESCRIPTION OF THE SEVERAL VIEW OF THE DRAWINGS

Reference will now be made, by way of example, to the accompanyingdrawings, in which:

FIG. 1 shows a neutral section insulator embodying the presentinvention;

FIG. 2 shows a part of a neutral section insulator embodying the presentinvention;

FIG. 3 is a more detailed drawing of FIG. 2;

FIG. 4 shows a connection member used in an embodiment of the presentinvention;

FIG. 5 shows a neutral section insulator embodying the presentinvention;

FIG. 6 shows front and side views of the neutral section insulator shownin FIG. 5;

FIG. 7 shows how the PTFE rails are arranged in an embodiment of thepresent invention; and

FIG. 8 shows an embodiment of the present invention with a modifiedsurface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a neutral section insulator 1 embodying the presentinvention. The neutral section insulator 1 includes an elongateinsulator body 10 moulded from an insulating material such as aglass-fibre reinforced epoxy composite with a 45% glass fraction. Theouter surface of the insulator body 10 can be chemically treated orcoated with a paint to improve its shedding ability and be generallyresilient in adverse environmental conditions,

The neutral section insulator 1 also contains a connection member 2 byway of which it connects to adjacent conductor ends. As shown in FIGS. 2and 3, in one embodiment of the present invention, the connection member2 is a U-shaped copper member embedded within the insulator body 10 withits legs 3, 4 (hereinafter referred to as conductor tails) protrudingtherefrom and lying adjacent to the conductors on either side of theinsulator body 10. One of the conductor tails 4 is connected to an endof the conductor line using conventional splices, for example, whilstthe other conductor tail 3, although usually redundant, can be used asan arcing horn if required. If there is any wear on the conductorsection into which the neutral section insulator is being fitted, theend face of the connecting conductor tail 4 can be filed accordingly sothat a step height change between the neutral section insulator and theconductor section can be avoided.

A connection member 2 used in an embodiment of the present invention isshown in more detail in FIG. 4 in which FIG. 4 a is a perspective view,FIG. 4 b is a front view and FIG. 4 c is a side view, As can be seenmost clearly from FIG. 4 a, pegs 5 are provided on the surface of theconnection member 2, equally spaced apart and so as to protrude from theouter surfaces of the conductor tails 3, 4 at corresponding positions.The pegs 5 are driven through the surfaces of the conductor tails 3, 4,before the connection member 2 is placed in the insulator body mold.When the mould sets, the pegs 5 remain firmly lodged in the insulatorbody walls, thus ensuring that the connection member 2 is held stronglywithin.

In one embodiment of the present invention, the dimensions indicated inFIG. 4 may be as follows: a1=30 mm, a2=100 mm, a3=17.09 mm, a4=200 mm,b1=46 mm, b2=34.19 mm, b3=22.37 mm, c1=20 mm, c2=10 mm, and d=2.5 mm. Inaddition, in such an embodiment, the radii of curvature e and f are 23mm arid 11.19 mm, respectively.

In an embodiment of the present invention, the profile of the neutralsection insulator 1 is matched with those of the copper conductors withwhich it is to be used on its either side by aligning the neutral axesof the neutral section insulator 1 and the copper conductors. This isachieved by designing the profile of the neutral section insulator 1such that its neutral axis is as low as reasonably practical, such as,for example, to lie only 12 mm above the neutral axis of adjacentconductors. Furthermore, the height of the insulator body is increasedso that the stiffness of the neutral section insulator 1 matches that ofthe conductors on its either side in both the vertical and horizontalplanes.

To achieve these criteria, a neutral section insulator 1 embodying thepresent invention can be designed as shown in FIG. 5, in which FIG. 5 ais a front view of the neutral section insulator 1, FIGS. 5 b, 5 c and 5d are cross-sections respectively taken on line A-A, line B-B, and lineC-C, and FIG. 5 e shows an outer view of one face of the neutral sectioninsulator 1. As most clearly seen from FIGS. 5 b to 5 d, when in use,the profile of the neutral section insulator 1 would be streamlined withthose of the conductors lying adjacent to it.

In one embodiment of the present invention, the dimensions indicated inFIG. 5 are as follows: g1=24.5 mm, g2=20.7 mm, g3=12 mm, g4=37.6 mm,g5=49 mm, g6=46.52 mm, g7=60 mm, g8=147.59 mm, g9=52.41 mm, 910=47.59mm, h1=10 mm, h2=19.5 mm, h3=25.93 mm, h4=29 mm, h5=18.05 mm, h6=33 mm,h7=19.24 mm, h8=23 mm, and h9=46 mm. In addition, in such an embodiment,the angle i of the sidewalls of the neutral section insulator 1 is 12°.The radii of curvature in this embodiment are as follows: j1=5 mm, j2=5mm, j3=1.5 mm, j4=200 mm, j5=24.5 mm, j6=8 mm, j7=11.19 mm, j8=22.06 mm,j9=8 mm, j10=1.5 mm, j11=1.5 mm and j12=8 mm.

FIGS. 6 a and 6 b show respective front and side views of an embodimentof the present invention. As can be seen from FIG. 6 a, two rails 6, 7are embedded in the running surface of the neutral section insulator 1.As these rails 6, 7 lie parallel to the conductor at each end of theneutral section insulator 1, they provide a continuous surface againstwhich the pantograph can run. By virtue of being made of a low frictionmaterial, such as PTFE, the rails pose less frictional drag to thepantograph compared to when it traverses the length of the conductors,thus helping to reduce wear of the pantograph and insulator body 10. Thewear characteristics of the rails can be improved by incorporating glassbeads in the PTFE. As the ends of the neutral section insulator 1 areturned up in a vertical direction, so too are the leading ends of therails 6, 7, (as can be seen most clearly in FIG. 7) which ensures thatthe pantograph attaches to the rails 6, 7 without hitting them.Furthermore, by virtue of being guided by the conductor tails 3,4, ontothe rails 6, 7, the pantograph attaches to the neutral section insulator1 in a fluid and smooth manner.

In one embodiment of the present invention, the dimensions indicated inFIG. 6 are as follows: k1=1706 mm, k2=200 mm, k3=100 mm, k4=21.6 mm,k5=37.6 mm, k6=49 mm, 11=57.5 mm, 12=18.43 mm, and 13=23 mm.

FIG. 8 shows an embodiment of the present invention with a modifiedsurface. Specifically, a semiconductor tape is attached to the spine ofthe neutral section insulator 1, which has the effect of spreading theexcess charge associated with arcing by conducting it along the lengthof the neutral section insulator 1. Furthermore, electrical plates(barriers) 11 or “sheds” are attached to the spine of the neutralsection insulator 1 in order to increase the effective electrical pathlength of the neutral section insulator 1. In an embodiment of thepresent invention, the barriers are made from epoxy resin with choppedstrand glass fibre reinforcement. However, they could be made of anyother appropriate material that is waterproof and non-conducting. It isdesirable to make the surface of each barrier as spherical as possiblesince the presence of any sharp corners would lead to concentration ofan electric field, and the undesirable scenario of a corona discharge.As can be seen from FIG. 8, the electrical barriers in an embodiment ofthe present invention are semi-spherical in shape with slots where theyare attached to the spine of the neutral section insulator 1. In anembodiment of the present invention, the barriers are spaced, and notnecessarily periodically, at a distance of 100 mm or greater. It hasbeen found that, for the voltages that the neutral section insulator 1is subjected to when in use, a barrier spacing of less than 100 mmbecomes transparent to an electric field, which will “jump” this gap.

It can be understood that, when in use, the neutral section insulator 1is exposed to different environmental conditions. Specifically, it isundesirable if a condensation film should form on it since salt ions inthe film would cause electrical discharge to occur from the outersurface of the neutral section insulator 1. In order to avoid thisscenario, a trace heater is incorporated into the moulding of theinsulator body 10 in an embodiment of the present invention. Thefunction of the trace heater is best understood when the neutral sectioninsulator 1 is subjected to a “salt fog” test. This test involvesexposing the neutral section insulator 1 to a salt intensive vapourcloud in a specialised chamber so as to evaluate its dischargeproperties. The heater is used to increase the temperature of theneutral section insulator 1 above the dewpoint temperature of thecondensing vapour cloud so that it does not condense on the outersurface of the neutral section insulator 1, or if it does, it evaporatesquickly. Thus, by using a trace heater, it is ensured that no electricaldischarge occurs from its surface due to the presence of a condensationfilm thereon when the neutral section insulator is in use. The traceheater is a printed element on a substrate, for example, a 150 W heaterelement on a KaptonR strip. Temperature limiting resistors are formed onthe printed substrate bearing the heater and are connected in series tothe heater. The non-linear dependence of the resistance of theseresistors on the ambient temperature drastically limits the currentflowing therethrough at high ambient temperatures, thus allowing thetemperature of the neutral section insulator 1 to be dynamicallyregulated and maintained at the same value in extreme environmentalconditions. In an embodiment of the present invention, four suchtemperature limiting resistors are discretely formed along the length ofthe neutral section insulator 1, at equal intervals, so that the neutralsection insulator 1 is maintained at the same temperature along itswhole length.

Although a preferred embodiment of the invention has been described,alternative implementations are possible. For example, the connectionmember 2 need not be U-shaped and can be any other appropriate shape.Also, the connection member 2 can be lodged within the insulator bodyvia alternative means to the pegs 5 described hereinabove. If support isrequired in the mid-section of a neutral section insulator 1 embodyingthe present invention, the neutral section insulator 1 may be connectedto an overhead catenary system using insulation droppers attached to thespine of the section 1 via adhesive pads.

1. A neutral section insulator for use with an overhead railwayconductor line, which neutral section insulator is disposed between theends of said conductor line when in use, the neutral section insulatorcomprising an insulator body having a single, integral body to isolatethe ends of said conductor line from each other; wherein the profile ofthe neutral section insulator is designed such that, when the neutralsection insulator is in use, its neutral axis is aligned closely withthe neutral axis of the conductors on its either side and the height ofsaid insulator body is chosen so that the stiffness and the dynamic massof the neutral section insulator closely match those of the conductorson its either side in both the vertical and horizontal planes, andwherein a semiconductor tape is attached to a spine of the neutralsection insulator.
 2. A neutral section insulator for use with anoverhead railway conductor line, which neutral section insulator isdisposed between the ends of said conductor line when in use, theneutral section insulator comprising an insulator body having a single,integral body to isolate the ends of said conductor line from eachother; wherein the profile of the neutral section insulator is designedsuch that, when the neutral section insulator is in use, its neutralaxis is aligned closely with the neutral axis of the conductors on itseither side and the height of said insulator body is chosen so that thestiffness and the dynamic mass of the neutral section insulator closelymatch those of the conductors on its either side in both the verticaland horizontal planes, wherein electrical plates are attached to a spineof the neutral section insulator, and wherein the plates are spaced at adistance of 100 mm or more.
 3. A neutral section insulator as claimed inclaim 2, wherein each of said electrical plates is made of epoxy resinwith chopped strand glass fiber reinforcement.
 4. A neutral sectioninsulator for use with an overhead railway conductor line, which neutralsection insulator is disposed between the ends of said conductor linewhen in use, the neutral section insulator comprising an insulator bodyhaving a single, integral body to isolate the ends of said conductorline from each other; wherein the profile of the neutral sectioninsulator is designed such that, when the neutral section insulator isin use, its neutral axis is aligned closely with the neutral axis of theconductors on its either side and the height of said insulator body ischosen so that the stiffness and the dynamic mass of the neutral sectioninsulator closely match those of the conductors on its either side inboth the vertical and horizontal planes, wherein electrical plates areattached to a spine of the neutral section insulator, and wherein theplates have spherical surfaces.
 5. A neutral section insulator asclaimed in claim 4, wherein each of said electrical plates is made ofepoxy resin with chopped strand glass fiber reinforcement.